Cathodic plug

ABSTRACT

1. An improved electrolytic cell including: a cell adapted to accept a series of anode members and corresponding cathodes provided with cathode members; and an insulating medium disposed at the lower portion of such cell; said cathode member being provided with a spherical portion having a flat contact surface for directly contacting the interior wall of the cell and a threaded shank portion depending therefrom, extending through the cell wall to the exterior of said cell; fastening means engaging said threaded shank to fixedly position said cathode member with respect to said cell in a manner enabling said cathode member to co-act with a layer of mercury disposed at the lower portion of said cell to thereby form a mercury cathode.

H. H. TIEDEMANN CATHODIC PLUG Nov. 5, 1974 Filed Aug- 3 1972 "United States Patent O 3,846,272 CATHODIC PLUG Herman H. Tiedemann, Linden, NJ., assignor to GAF Corporation, New York, N.Y. Filed Aug. 3, 1972, Ser. No. 277,653 Claims priority, application Germany, Sept. 11, 1971, P 21 45 507.2 Int. Cl. C22d I/04 U.S. Cl. 204-219 3 Claims ABSTRACT F THE DISCLOSURE A cathodic plug suitable for use in an electrolytic cell for the manufacture of a halogen gas, such as chlorine. The cathodic plug is rendered stress free during its manufacture by means of annealing and subsequent air cooling. The ultimate use of such treated cathodic plug in an electrolytic cell eliminates the deposition of crystalline matter at the Working end of such plug. The plug is provided with an upper dome shaped portion and depending shank of suicient size to be xedly positioned through the electrolytic cell wall.

A cathodic plug suitable for use in an electrolytic cell for the manufacture of a halogen gas, such as chlorine. The cathodic plug is rendered stress free during its manufacture by means of annealing and subsequent air cooling. The ultimate use of such treated cathodic plug in an electroyltic cell eliminates the deposition of crystalline matter at the working end of such plug. The plug is provided with an upper dome shaped portion and a depending shank of sucient size to bev xedly positioned through the electrolytic cell wall.

The present invention is directed to a cathodic conductor, hereafter referred to as a cathodic plug; more particularly, to a cathodic plug that is utilized in connection with an electrolytic cell for the production of a halogen gas, such as chlorine.

By way of background, the instant invention relates to an essential element forming part of such cell that is ernployed in the production of chlorine, as by the electrolysis of sodium chloride. In such an operation, graphite anodes and cathodes of mercury are introduced into the electrolytic cell, and in accordance with the arrangement shown, as for example, in my U.S. Pat. 3,471,383; there are provided a number of cathode contactors or plugs which function as conductors and serve as the means by which electrical current is carried through the bottom of the cell into contact with the solution.

The chlorine manufacturing process itself is carried out in a relatively large, iat cell that can vary from approximately 35 to 70 feet in length and is approximately 6 feet in width. lDepending upon the size of the cell in question, the number of cathode plugs required during operation of the cell can vary from about 150 to 500. Such plugs serve the very important function of providing a means by which electrical current is introduced into the cell from a source in a safe and prudent manner, without in any way endangering the safety of the operation.

A series of heavy anodes which have corresponding cathode plug members are disposed within the cell, and a body of mercury is disposed in the lower portion of the electrolytic cell and completely surrounds the upper portion of the cathode plugs positioned in the cell and held in place by suitable fastening means. The plugs are insulated from the cell by means of a rubber blanket (which coats the entire lower portion of the cell) and are countersunk below the surface of the rubber for about 1 mm. The rubber insulation is usually about @ya of an inch thick. Durig normal operation the plug is covered with a film of mercury approximately 2 to 3 mm. thick at the ICC center; and with this arrangement, the salt solution is prevented from coming into contact with the steel vessel or the plug itself, and consequently, any adverse effects are eliminated, i.e. producing hydrogen, a highly combustible and explosive gas. The very nature of a rubber insulation overlapping the plug, as hereinafter described, enables the mercury to positively cover the cathodic plugs at all times and acts as a barrier between the steel cell and salt solution.

'It is well known in the art to manufacture cathodic plugs by means of round steel stock which is worked upon by drop forging at one end, in such a way, that after continuous peening, the end worked upon becomes blunted and develops into a mushroomed, uneven, broad mass. 'I'he surface so produced, permits the mushroomed portion (after machining into a sphere) to offer a good contact area with the mercury bath serving as an excellent electrical conductor.

The plug when ultimately machined and ready for use, is a unitary structure having a head or upper portion as well as, a depending shank which can be about 1 to 1% inches thick, it is this shank, that is suitably threaded and extends through the wall to be iixedly attached to the cell by a fastener, such as a nut. The spherical portion is disposed interior of the cell and serves as the working end of the plug for the conduction of electric current into the solution undergoing electrolysis.

As a result of the forging operation discussed above, stresses are formed in the shank and especially in the head portion of the plug, due to an alteration of the molecular structure of the material being worked upon. Up until the instant invention such stresses have always remained in the cathodic plug, and a number of shortcomings attributable to such stresses have always been present in the halogen gas manufacturing operation. Firstly, during electrolysis, such plugs had a tendency to corrode quite readily around the edge portions of the sphere, interior of the cell. Secondly, a secondary chemical reaction within the entire circuit, resulted in the deposition of hard large granular crystals of salt over the entire surface of the spherical head with particular concentration of deposition at the perimeter of the plug surface.

With these defects, substantial shortcomings in the overall operation of the electrolytic process took place. Insofar as the latter defect is concerned, the salt crystals as they broke up, disturbed the mercury lm continuity at the lower portion of the cell and resulted in an uneven mercury body exhibiting ripples. This, in turn, greatly affected the conduction of current from the cathode to the anode and at times, short outs and other breakdowns occurred which necessitated a closing down of the cell, drainage of the system, and the need to scrape the plug members free of crystals to thereby eliminate surface defects. This, in turn, resulted in a substantial loss of production time and labor costs in maintaining the cells.

.Replacement of the electrolytic cell with a new cathode plug is an expensive procedure. 'In conventional practices, the electrolytic cell covers are removed after the system has been shut down and then there is a rather tedious operation of removing the crystals that have been formed by chipping or otherwise, and thereafter the interior is completely washed down and cleaned.

In the event complete corrosion has taken place, the cathode plugs themselves had to be replaced, in which case, the fastening member retaining the plug, i.e. nut, is removed and the plug itself is forced out of the lower portion of the cell. Once replacement has taken place, the cell is reassembled and placed back into operation.

In a typical situation, as many as four days are required to replace and clean several hundred plugs and during this time, the cell is producing nothing.

From a review of the prior art, it appears that up until the present invention very little attention has been focused upon the elimination of the aforementioned defects by stress removal in the working portion of the cathode plug. Industry has completely accepted the loss of metal from the plug perimeter, as well as the deposition of salt through secondary reactions, as part of the expected cost of production and expected downtime. Industry as a whole appeared to be quite complacent in accepting these undesirable defects; however, it is only with the discovery of the instant invention that Applicant has found that the stress condition of the cathode plug is directly related to the eiciency and trouble free production of gas in an electrolytic cell. An improved stress free plug, as hereinafter disclosed, performs all of its necessary operative functions of former plugs, but in addition, especially contributes to the elimination of salt clustering at the perimeter of the plug.

The gap between the surface level of mercury and the anode is lled with brine or a salt solution which is being electrolyzed by the electric current being conducted through the cathodic plug to the anode. When the mercury level between the salt solution and the anode is uniform in disposition, the electrolytic process continues very eiciently. However, any disturbance in the mercury level can cause such mercury to ripple and occasionally touch the anode block resulting in a shorting out of the cell. Obviously, in the presence of high amperage, for an example, in the range of 100,000 to 200,000 amps per cell, such contact can produce very fatal results with subsequent large surges of power in the cell causing over-heating and melting of the electrical circuitry.

It is well understood that in the presence of a corrosive environment, metal deterioration is accelerated by stressing. In this connection, for example, a piece of flat steel bent and deformed and placed in a corrosive environment corrodes at a much faster rate than a piece that has not been so deformed. This is explained by the fact that the rate of corrosion across the stressed surfaces takes place at a faster rate than across non-stressed surface and is accelerated by an electrolytic effect caused by a higher electrical potential in the stressed areas versus the nonstressed areas.

`The instant invention has recognized the need to provide for an improved cathodic plug which functions in a manner similar to existing plugs and is compatible with existing electrolytic cells, while at the same time, capable of developing favorable process operations while eliminating any of the aforementioned problems.

An approach toward overcoming the aforementioned effects of stress can take the form of employing stress free raw materials, i.e. steel which is machined down to an appropriate size for use in specific electrolytic cell applications. However, the use of large diameter round stock which is machined down to a much smaller appropriate size can be very costly. Obviously, such an approach eliminates the forging operation and thereby overcomes the adverse stress condition created by forging in the first instance; however, it would be most uneconomical to employ this technique for most applications. For example, where head portions are conceivably 8 inches or more in diameter and the shank depending therefrom between 1 and 11/2 inches in diameter, the cost for a plug becomes most exorbitant.

Accordingly, it is the main object of the present invention to eliminate the shortcomings of the prior art.

Still another object of the present invention is to employ an improved cathodic plug compatible for use with an electrolytic cell suitable for the manufacture of a halogen gas, i.e. chlorine, which plug is free of any stresses that can negatively contribute to the operation of the cell.

Still another object of the present invention is to produce chlorine in an electrolytic cell in which the cathode plug serves as a conductor of electricity and is adapted to coact with the anode member during electrolysis; such cathode plug being free from any physical factors which contribute to the deposition of salt crystals at its periphery.

A further object of the present invention is to provide a simple, efficient and economic method for producing cathodic conductor plugs suitable for use in electrolytic cells where such plugs are free of stresses.

Still another object of the present invention is to provide a cathodic plug that is readily manufactured and free from the stresses throughout its entire unitary structure because of annealing of such plugs at select temperatures for designated times.

Still a further object of the present invention is to improve the manufacturing process by which chlorine is produced using electrolysis, where improved cathode conductors in the form of plugs increase the longevity and minimize the downtime for such operation.

Briefly the present invention contemplates an improved electrolytic cell including a cell adapted to accept a series of anode members and corresponding cathodes provided with stress free cathode members; and an insulating medium disposed at the lower portion of said cell; said cathode member is provided with a spherical portion disposed interior of the cell and a threaded shank portion depending therefrom, extending through the cell wall to the exterior of said cell; fastening means engaging said threaded shank to fixedly position said cathode member with `respect to said cell in a manner enabling said cathode member to coact with a layer of mercury disposed at the lower portion of said cell to thereby form a mercury cathode.

Also within the scope of the instant invention is a cathodic member including an upper spherical portion having an elongated shank portion depending therefrom and is subtantially stress free in at least the area of said upper portion.

The construction and method of operation of the instant invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the figures of the accompanying drawings showing the cathodic plug in accordance with the invention.

In the drawings:

FIG. 1 is a fragmented diagrammatic view of a typical cellashowing the instant invention.

FIG. 2 is a side elevation view of the cathodic plug showing the stress free dome portion.

According to FIG. 1, the instant invention contemplates a series of plugs 1 which are adapted to seat in the electrolytic cell 6. The plug 1 is detailed in FIG. 2, where a suitably machined steel bar is worked and machined to size, resulting in a unit having an upper spherical portion 3, and a depending shank portion 2. The lower portion of the shank 3 is provided with a suitable number of threads 4 along part of its length. The spherical portion 3 is the working end of the plug 1 and is the most sensitive portion of the cathode plug 1, and will be discused in more detail hereinafter below.

Applicant has discovered that by means of careful and proper annealing, the stress characteristics of the anode plug 1 produced during its manufacture, are so altered, that the defects as described hereinbefore, become almost nonexistent or are completely minimized. Unexpectedly, applicant has found that by annealing the cathodic plug 1 in a furnace at a temperature of between 1100 to 1200 F. for a period of approximately 2 hours, the character of the cathodic plug 1 is changed during the annealing operation. The annealed plug 1 after such heat treatment is withdrawn from the furnace and cooled to ambient tem\ perature by ordinary air cooling. Thereafter, the plugs are ready for insertion into the electrolytic cell and. adapted to function in the usual manner.

Referring in greater detail to FIG. 1, there is shown a basic sectional layout for a typical mercury type chlorine caustic cell. Anodes 5, of which several are shown, are suspended from the ceiling 7 of the cell 6 such that their height may be adjusted. Suspending means are not shown, except that each block has an upwardly extending column passing through the ceiling 7 of the cell 6. Electric current is supplied from a source 8 distributed through several conductors 9 to the several anodes 5. Cathodic plugs 1 are shown resting on the floor 10 of the cell 6, these being electrically connected through suitable conductors 9 to the negative side of the current supply 8' and held in position by fasteners 13, i.e. nuts. An insulating blanket 14, made of rubber or other suitable material, is disposed at the bottom of the cell floor 10.

The cathodic plugs 1, which are in multiple and preferably in about the same number as the anode blocks 5, supply current to the cathodic layer of mercury 11. The latter ows through an inlet (not shown) into the cell 6 and moves to the left along the oor of the cell 10 in a horizontal layer 11 to an outlet (not shown). From the latter, the mercury which by now is an amalgam with sodium is taken to the denuder (not shown) for mercury recovery. The insulating blank 14 acts as a barrier between the steel cell 6 and brine solution 12. The same system ebviously is applicable to treatment of other salts, especially other alkali metal halides besides sodium chloride.

The strong brine 12 of the salt being electrolyzed is supplied through inlet line (not shown) at the right of the cell. It flows along the cell 6 from right to left as electrolysis takes place. Gaseous chlorine is evolved from the top of the cell 6 through an outlet (not shown) and 'the spent brine passes out through another outlet (not shown). The sodium, of course, is converted primarily to NaOH.

It follows with the present invention the method of producing chlorine by electrolysis is greatly enhanced by the elimination of any deleterious eiects which can result from the presence of stressed cathodic plugs. The acceptance of such undesirable consequences up until the instant invention was considered part of the day-to-day operation with very little consideration given to the elimination of such defects. The introduction of the plug delined by the present invention clearly adds to the eiiciency of the process and is adapted to operate without any secondary reaction during the electrolysis.

While the present invention contemplates use with the steel structure and a cathodic plug for use in the electrolyzation of chlorine gas by means of the introduction of a high current surging in a brine solution. It is suggested that the scope and the intent of the present invention is not to be so limited.

It is suggested that the operation to which the instant invention is directed, through being quite simple and quite understandable, it has never been successfully introduced previously.

It will be understood that certain changes may be made in the construction or arrangement of the cathodic plug electrolytic cell which is disclosed herein without departing from the spirit and scope of the invention as defined in the appended claims. In this respect, for an example, the use of the term spherical is not intended to be limited to usage for only a sphere or a part thereof. Any dome or arcuate shape of regular or irregular contour is deemed to fall within the scope of the present invention.

What is claimed is:

1. An improved electrolytic cell including: a cell adapted to accept a series of anode members and corresponding cathodes -provided with cathode members; and an insulating medium disposed at the lower portion of such cell; said cathode member being provided with a spherical portion having a flat contact surface for directly contacting the interior wall of the cell and a threaded shank portion depending therefrom, extending through the cell wall to the exterior of said cell; fastening means engaging said threaded shank to ixedly position said cathode member with respect to said cell in a manner enabling said cathode member to co-act with a layer of mercury disposed at the lower portion of said cell to thereby form a mercury cathode.

2. An improved electrolytic cell as claimed in claim 1, wherein said cathode member coacts with a mercury layer disposed approximately 1 mm. above the upper surface of said head portion to form a mercury cathode adapted to carry electrical current into said electrolytic cell.

3. An electrolytic cell as defined in claim 1 wherein said cathode member has been annealed.

References Cited UNITED STATES PATENTS 3,502,561 3/ 1970 Rache et al 204-250 X R 2,545,376 3/1951 Ornhjelm 204-219 X R FOREIGN PATENTS 705,541 3/ 1954 Great Britain 204-250 667,477 3/ 1952 Great Britain 204-250 JOHN H. MACK, Primary Examiner D. R. VALENTINE, Assistant Examiner U.S. C1. X.R. 204--250 

1. An improved electrolytic cell including: a cell adapted to accept a series of anode members and corresponding cathodes provided with cathode members; and an insulating medium disposed at the lower portion of such cell; said cathode member being provided with a spherical portion having a flat contact surface for directly contacting the interior wall of the cell and a threaded shank portion depending therefrom, extending through the cell wall to the exterior of said cell; fastening means engaging said threaded shank to fixedly position said cathode member with respect to said cell in a manner enabling said cathode member to co-act with a layer of mercury disposed at the lower portion of said cell to thereby form a mercury cathode. 